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We currently average around $200/month electric and $48/month for gas (1300sf).

Well you have go into this build focusing more on comfort, and not savings, it will help you in your ability to concentrate on the "total" outcome. You have to have a comparison to something to figure savings,your building a new home. I by no means want to say you cannot fulfill your dreams of how your would like the outcome to be. Houston is a beast, I have seen a lot of good sincere jobs done here in good faith, to achieve the very best efficiency of the total home, fall short of the homeowners expectations, and really only you can personally sense what your expectations are. I do agree, although you don't see many in Houston "don't know why" with installing a whole house dehumidifier, in 30 years I have never personally come across a customer with a dehumidifier in their home, I think if the $$$ allow that would be a very good investment, just makes sense for this local.

PS...I like to always throw this in, I know the zonies don't like this, but if your zoned system goes down, your dead in the water, if you have two systems you can be cool till the a/c guy gets out, which in the summer in Houston, could be a bit. But on the brighter side, if your zoned system goes down, you can always stay at a Holiday Inn Express, the kids will Love the pool.

__________________________________________________ _______________________
“Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

"The rest will be a simple matter of execution..."
good that you added the smiley..execution may not be
simple.

It never is, but execution will matter less if I get the wrong package in the spec up-front. For my nickel, I want to know the trade-offs, then watch the install like a hawk. The framing, flashing, insulation and window install will also be watched very, very closely.

my worry is that you'll encounter quite a bit of the 500 sq ft per ton hvac sizing.
so prepare yourself for that battle, the two systems are better than a single
zoned system, and really work on if heat pumps cost more to operate than
gas.

Hence the quest to seek advice and information. I'm especially worried about the first issue. I could solve a fair bit of the worry by just specifying a Mitsubishi Ducted system, but then I'd wonder about how high of a premium I am paying for the one (or two) guys in town that carry the gear (let's give them the benefit of the doubt that they understand VRF if they are willing to carry it down here...).

understand that rather than downsize or even properly size the hvac systems
the goal will change to more expensive equipment set to run in lower speeds to
achieve less tons. you pay for the upcharge, extra system & cost to maintain &
operate for a very very long time. make your hvac choices a priority.

I hope that I haven't given anyone here the impression that HVAC choices aren't a priority! You hit the nail on the head, though, of what I sense are the key variables at play (greater expense for more efficient operation, but that may be a significant net increase in cash costs).

whole house dehumidifiers can be set up to bring in needed fresh air.
that is the route I'd go.

The inexpensive Panasonic ERVs are still in the running, but if we go with a conventional set-up, we will most likely go this route.

windows are the weakest part of the wall, the lower the shgc & ufactors are,
the better the window. itrw purchasing different shgc & ufactors for different
sides (orientation) of the house is another problem. unless you plan to make
sure yourself that the right window is installed on the west side vs north side
it is better to buy the same window for all sides.
just what I've encountered over the years.
don't believe that the installers
actually understand the difference between anything other than window size.
and invest a little time in reading flashing directions that come with each window unit.
you can be sure that the installers will do the flashing the way they have always
done it. we have lots of water intrusion here from that old X cut into the housewrap.
good flashing info on each window...if someone reads it and makes sure it is done
properly.

what is your insulation package?
for walls, I perfer foam sheathing on exterior, conventional insulation in walls
and air tight drywall approach to interior.

you say ducts in conditioned space...can you explain this a bit?
fur downs? foamed attic?

Unvented attic, open-web trusses. The most relevant near-term decision is how many air handlers we need and where they need to be located (e.g., Mitsu VRF or multiple systems? We need an air handler on the first floor. Carrier or Lennox zoned? Not so much.

with ducts & equpment not in the attic..you'll save on utility costs.
if possible to do, it is a good step towards performance. putting ducts in
conditioned space nets about a 25% energy savings.

recessed lights should only be ICAT insulation contact air tight. IC are cheaper
but an opening to the hot humid attic. retrofitting IC to ICAT is costly. better
to buy ICAT to start with.

Unvented attic means that any can lights are not going to be a source of heat loss or a weak spot for moisture accumulation.

sealing any penetrations from attic into living space should be priority also.
oversized cuts for bath fans, recessed lights, stove venting, return or supply
air..these areas are easy to find if you look for the leakage sites prior to
insulation in attic.

Well you have go into this build focusing more on comfort, and not savings, it will help you in your ability to concentrate on the "total" outcome. You have to have a comparison to something to figure savings,your building a new home. I by no means want to say you cannot fulfill your dreams of how your would like the outcome to be. Houston is a beast, I have seen a lot of good sincere jobs done here in good faith, to achieve the very best efficiency of the total home, fall short of the homeowners expectations, and really only you can personally sense what your expectations are. I do agree, although you don't see many in Houston "don't know why" with installing a whole house dehumidifier, in 30 years I have never personally come across a customer with a dehumidifier in their home, I think if the $$$ allow that would be a very good investment, just makes sense for this local.

PS...I like to always throw this in, I know the zonies don't like this, but if your zoned system goes down, your dead in the water, if you have two systems you can be cool till the a/c guy gets out, which in the summer in Houston, could be a bit. But on the brighter side, if your zoned system goes down, you can always stay at a Holiday Inn Express, the kids will Love the pool.

I think that we will end up being a lot of people's best (and worst) customers. I've got the budget to pay premiums where it makes sense, but I have to have confidence that the premium is worth it. Given the expected cost-of-cash, I am largely indifferent between paying $10k more in order to save $50/month. What I don't want to do is spend $10k more in order to spend $100/month more because the system is both expensive AND inefficient. I think that I can get to comfortable a number of different ways, so what I'd like to know is what the relative merits are for each of the major paths.

TJI rafters (most likely) with polyester mesh stapled across. The fiberglass is then blown (BIBS) into the rafter bays for insulation. We'll need to figure out whether we care about putting in a thermal break on the exterior decking (I'm less inclined to do it given the depth of insulation). We will need to add blocking and probably a small knee wall where the rafters intersect the primary wall assembly. There will be a fair bit of spray foam in there. We can't fully get away from SPF, but my wife is sensitive to many household chemicals, so I am not wanting to risk the chance that the SPF crew has a bad day going with SPF as the primary insulation. I may change my mind after touring a few more SPF-insulated homes, but she had problems with "ambient odor" in the house we visited last week, and I did not tell her it was an SPF job.

If your are curious, there are a few articles out there on the "PERSIST" and/or "REMOTE" methods (REMOTE is an Alaskan-oriented derivative). You essentially trade a lot of Ice & Water Shield for the SPF. Expensive and it doesn't even provide any insulation. That's why I am heading more into the "tape the seams" method, above.

I've got the budget to pay premiums where it makes sense, but I have to have confidence that the premium is worth it.

And I can appreciate that statement, and of course your a smart man I can tell, so you will have to gain that confidence strictly from data sheets of all kinds.
I don't like comparing A/C systems to cars, but sometimes I can justify doing this. Your building a 1/4 mile race car out in your garage, and of course you have studied the build for years, you have a certain amount of dollars to spend, and all the data sheets say you should be able to get a 10 second car out of this build, it's done and your @ 10.75, not quite what you wanted but can you live with that? My message here is, "sometimes" beyond data, equipment, and dollars, common sense and experience comes into play, to tweak any project.

__________________________________________________ _______________________
“Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

And I can appreciate that statement, and of course your a smart man I can tell, so you will have to gain that confidence strictly from data sheets of all kinds.
I don't like comparing A/C systems to cars, but sometimes I can justify doing this. Your building a 1/4 mile race car out in your garage, and of course you have studied the build for years, you have a certain amount of dollars to spend, and all the data sheets say you should be able to get a 10 second car out of this build, it's done and your @ 10.75, not quite what you wanted but can you live with that? My message here is, "sometimes" beyond data, equipment, and dollars, common sense and experience comes into play, to tweak any project.

If I hit 10.75, then I'll most likely be pretty ecstatic, especially if I know where the 0.75 went (e.g., lower compression rings since they were cheaper). What I don't want is a car that is built for a 7 second run, but where the engine blows up before the lights go green...

Let me perhaps get more clear about the various options under consideration:

1) Single stage AC + (small) Gas furnace - standard Houston practice, we have this in our current home. Probably two units (one up and one down). If I don't ask for better, this is likely what every contractor my builder polls will spec.
2) Single-stage Heat Pump - as above, but without the gas furnace. Electricity runs $0.11/kWhr (more or less) and gas is $0.80/Ccf (more or less). Higher acquisition cost vs. the AC unit, but indeterminate vs. the package.
3) High-efficiency, two-stage iterations of both of the above. Somewhat likely to get "upsold" into a higher tonnage unit(s) to handle peak loads, while the lower speed stage may or may not still be overkill for our average needs. Ductwork and other items also having to be sized to the peak airflow means more added expense.
4) VRF Heat Pump (Japanese) - Mitsubishi can operate more than one air handler internally (great!), but there are few contractors locally who work with these units (not great), and the ones that seem to work in a ducted application (we need high performance filtration) seem to only have mid-market efficiency ratings. I've read a studies done by FSRC, among others, on these types of units to see what the practical efficiency is. This is still an open question.
5) Variable-Speed Heat Pumps (Team America) - Lennox or Carrier both offer variable speed heat pumps, but zoning is done via dampers (as far as I can tell). This complicates the ductwork, and the Carrier units seem to have had some teething pain. The Lennox units are even newer.

One of the issues I am especially curious about getting expert advice on: would we need dedicated dehumidification (e.g., Ultra Aire XT105H or XT155H) if we went the VRF/Greenspeed route?

I like the idea of using the DHW source as the back-up or even primary heater, though finding someone locally who can do it may be a challenge. There are also people whose opinion I respect who say that I would want to keep the water that I use for heating separated from my potable hot water (this was in the context of in-floor hydronic systems, but the general principle probably applies...).

Thanks!

A good start is building a home that has a natural air change in 4-5 hours during cold windy weather. This means that during the windy weather you will get enough natural fresh air to not need mechanical fresh air. It means that you will get little or no natural fresh air ventilation during the mild calm weather. With your mild weather, there is little or no payback for an ERV. Also having a kitchen exhaust hood, clothes drier, and bath fans exhausting air when in use need make-up air to function.
A solid high SEER a/c properly setup will maintain <50%RH during moderate to high cooling loads. There are many days that the outdoor dew points are high but sensible cooling loads are low or none. Fresh air ventilating and moisture from the occupants for a home your size needs 4-5 lbs. of dehumidification per hour without any significant sensible cooling to maintain <50%RH. This makes the whole house ventilating dehumidifier like the Ultra-Aire XT105 an ideal ventilation, humidity control device.
The multi-speed a/cs are expensive and unable to maintain <50%RH during the low/no cooling load conditions. This also av oid any need for overcooling during low cooling loads. Also the a/c can be turned off for extended periods and the dehumidifier will maintain <50%RH for minimal electricity.
Looking forward to more discussion.
Regards TB